It can be important to track people and devices indoors, but an indoor environment introduces factors that make such tracking difficult. A number of approaches have been used in the past. Cell technology can use the power from various towers to try and triangulate any position. Wifi access points have also been used. If the location of the Wifi access point is known before hand, then the received signal strength from each access point can be used to triangulate and estimate the position.
Global Position System (GPS) has been used in a number of different applications, from tracking containers to providing positioning for autonomous robotic vehicles. One thing that GPS cannot do, however, is provide positioning indoors because the frequency and power of the GPS satellite signal is not strong enough to penetrate the roof and walls of typical building construction materials. Various technologies have attempted to combine GPS data (taken when a device was outside) with other information, such as Cell triangulation, Wifi and accelerometer data to try and estimate indoor position with greater accuracy.
Another approach to determining indoor positioning is to use previously installed nodes to record signal strength—using the proximity to these sensors to establish approximate locations.
Each of these methods suffers from poor accuracy. In addition, there are some applications where it is difficult to pre-position multiple pre-installed nodes inside the building where positioning is desired. Systems that require prior infrastructure indoors do not work in, for instance, emergency or military situations; these types of applications often do not use positioning for this reason and instead try to use remote cameras for monitoring. Remote cameras, however, can only work when visibility is good.